Find out what to look for—and what to avoid—when choosing supplements

The market is flooded with supplements for just about every type of nutritional deficiency, so separating the good from the bad requires some know-how. Below, the experts have broken down which factors to seek out, like reputable brand names, and which to stay away from, like potentially dangerous additives, when shopping for vitamins.

Look for:

1. Reputable brands. "Brand names (including Nature Made, GNC, Nature's Bounty, etc.) have more on the line and are less likely to put together a formula that could be controversial or get them in trouble with the FDA," says Elizabeth Somer, RD. You can also check to see if the product has been certified by either the United States Pharmacopeia (USP.org) or NSF International (NSF.org). These are not-for- profit groups that monitor supplements for safety and purity. If you want to do extra research, the for-profit website consumer-lab. com tests hundreds of vitamins every year. Because vitamins lose potency over time or when stored at high temperatures (think direct sunlight), keep these factors in mind when you buy, and check packages for expiration dates.

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2. Few additives. "You're putting a multivitamin in your mouth every single day, so it's definitely a place to opt for purity," says Mark Hyman, MD. Some brands can contain gluten, lactose and other allergens, so be sure to check the list if you're allergic. Also, though most ingredients are considered safe, there's no harm in looking for something that has low levels of filler and dyes. Read the ingredients list—you don't want to see the words "flow agents" (a filler) or "hydrogenated oils," or a long list of colors. Some brands (such as Nature Made) also specify that they're preservative-free.

Avoid:

1. Any supplement that contains stimulants like caffeine or a long list of herbs. In high amounts, these can give you heart palpitations and even affect your nervous system. If you're already taking a multi plus calcium, vitamin D and omega-3 supplements, you probably don't need a specialty formula, which may contain these things.

2. Calcium derived from oyster shells. The label will state this; recent studies have determined that these formulas can sometimes contain lead.

Sara Reistad-Long is a freelance writer who specializes in health and well-being. She also blogs about food at SvelteGourmand.com.